CONCLUSION

Based on the results presented above, it is reasonable to conclude that the

interactions involved in PEC formation are predominantly electrostatic. The PEC formation process is influenced by a varity of parameters, including the

1 祄

a

1 祄

b

1 祄

c

1 祄

d

e f

211.3nm 217.8nm g

Figure 9. Atomic force microscopy images of polymer-insulin complexes at optimized charge ratio.

(a) Chitosan 100 kDa, (b) Trimethyl chitosan 100 kDa, (c) PEG(5k)40-g-TMC(100), (d) PEG(550)228-g-TMC(100), (e) Three-dimentional image of chitosan 100 kDa, (f) Three-dimensional image of PEG(550) -g-TMC(100), g) line scan size analysis of

PEG(550)228-g-TMC(100). The inserts are 1x1 µm for each image.

system pH, sequence of mixing, polymer/protein ratio and concentration, polymer molecular weight and structure, ionic strength, etc. Amongst all of these parameters, the most important factor appears to be the system pH. The order of mixing is polymer property dependent. With regard to chitosan, due to its poor solubility at neutral pH, the insulin solution should be added to chitosan solution to avoid precipitation. In contrast, the mixing order appears to have a negligible influence for TMC and PEGylated TMC copolymers. The polymer/protein ratio needs to be optimized individually. When the MW of chitosan and its derivatives were ≥25 kDa, soluble insulin complexes in the size range of 200-400 nm with spherical or sub-spherical morphology can be readily obtained by simply mixing two components at a specific pH and charge ratio. All of the insulin complexes were successfully freeze-dried without influcing the complex properties, by using sucrose as a lyoprotectant. These studies have contributed much to the understanding of PEC formation and complexation with insulin. This work will be furthered by performing intranasal absorption studies in animal models.

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